Magnesium base alloy



Patented Nov. 12, 1940 STATES MAGNESIUM BASE ALLOY No Drawing.Application November 13, 1939,

. Serial No. 304,120

'4 Claims.

The invention relates to magnesium base alloys.. It more particularlyconcerns alloys of this nature having a high degree of formabilitycoupled with other improved physical properties,

such as high tensile and yield strengths.

Magnesium alloys are enjoying increasing use in the structural artswhere a light weight metal is highly desirable, such as for use inmaking large castings, forgings, and the like. However,

the use of these alloys in the rolled form to make sheet metal articlesrequiring forming operations, such as bending, drawing, and the like,has not progressed as rapidly due to the fact that ingeneral alloys ofgood formability, permitting relal5 tively sharp bends to be madewithout the article developing external cracks, have inferiorcharacteristics as regards their tensile strength and yield strength.

It is, accordingly, the principal object of the invention to provide amagnesium base alloy which can be made into rolled sheet or the like,possessing a sufficient degree of ductility or formability at ordinarytemperatures to be sharply bent, drawn, or otherwise shaped, whilehaving greatly improved tensile and yield strengths.

Other objects and advantages will beapparent as the description of theinvention proceeds.

My invention resides in the discovery that a a magnesium base alloycomposed of from about 0.3 to 12 per cent of silver, 0.05 to 1 per centof calcium, and 0.1 to 3 per cent of manganese, the balance beingsubstantially all magnesium, is endowed with the afore-mentionedproperties. While the property of good formability or ductility, coupledwith increased tensile strength and yield strength is manifest over theentire range of composition indicated, I have found that in general thepreferred combination of properties, such as the most desirableductility for forming operations coupled with high tensile strength andgreatly increased yield in those alloys containing from between about0.5 to 6.0 per cent of silver, 0.2 to 0.3 per cent of calcium, and 1.0to 3.0 per cent of manganese.

The alloys containing the higher percentages of alloying ingredients,such as from between about 6 to 12 per cent of silver, 0.2 to 0.5 percent of calcium, and 1.0 to 3.0 per cent of manganese, while not havingas good ductility as those in the first mentioned range, do have a muchhigher yield and tensile strength, and are thus especially suitable foruse in casting operations. A preferred alloy having exceptionally goodductility and formability, as well as high tensile and yield strengths,is one containing about 4.0 per strength, is found cent of silver, 0.3per cent of calcium, and 2.0 per' cent of manganese.

The improvement in physical properties of my new alloy over that ofrelated alloys is illustrated by the ductility or formability of theabove 5 alloy as measured by a conventional bend test. In making thebend test referred toabove, a specimen of the alloy is subjected to abend and the minimum radius of a bend which can be I produced withoutfracture of the specimen at 10 room temperature is noted. The minimumradius thus obtained, expressed in terms of thickness of the specimenbeing subjected to the test, serves as a measure of the ductility orformability of the specimen. An annealed specimen of 15 my new alloy hada ductility of 2.5 times the thickness of the specimen when subjected tothe above test. An annealed specimen of this alloy was also found tohave a yield strength of 30,000 pounds per square inch and atensile'strength 20 of 41,000 pounds per square inch. In the cold rolledstate the preferred alloy was found to have an elongation of 6 per centin 2 inches, a yz'iid strength of 45,000 pounds per square inch, and atensile strength of 49,000 pounds per square 25 inch. Similarly, bothends of the composition range also exhibited correspondingly desirableproperty values.

The above quaternary alloy clearly has greatly improved properties overthose of the closely 0 related ternary alloys. As an illustration, theternary magnesium-manganese-calcium alloy having similar percentages ofmanganese and calcium as the above alloy, while having a ductility, asmeasured by the bend test of 3 times the 35 thickness of the specimen,had in the annealed state a yield and. tensile strength of only 21,000and 35,000 pounds per square inch, respectively. In the cold rolledstate this same ternary alloy had a yield and tensile strength of only31,000 40 and 11,000 pounds per square inch, respectively, with only a 2per cent elongation in 2 inches. My new alloy also shows improvedproperties over the related parent ternary magnesium-silvercalcium alloyhaving the same percentages of 45 silver and calcium as the aboveillustrated preferred alloy. This ternary alloy, while having aductility, as measured by the bend test, of 2.5 times the thickness ofthe specimen, had in the annealed state a yield and tensil strength of50 only 20,000 and 34,000 pounds per square inch, respectively, while inthe cold rolled state the yield and tensile strengths were only 39,000and 45,000 pounds per square inch, respectively. In addition, thisternary alloy had an elongation of only 2 per cent in 2 inches. Theimprovement in properties is also apparent when a comparison and tensilestrength of 44,000 and 50,000 pounds per square inch, but had anelongation of only 4 per cent in 2 inches. The above comparison showsthat the combined properties of the new alloy are always superior tothose of the related ternary alloys. 0

The properties set forth above under the term annealed were obtained byfirst rolling the alloys at a temperature between about 500 to 700 F.and thereafter annealing them at various temperatures through a range offrom 400 to 800 F. The properties selected were those of the annealedspecimens which exhibited the maximum elongation. The properties setforth under the term cold rolled were obtained by selecting specimens ofthe alloys which had first been hot rolled at a temperature of from 500to 700 F. to additional rolling in the cold state to bring about a totalreduction of from 2 to 10 per cent. The properties selected were thoseof the cold rolled specimens which showed the greatest tensile and yieldstrengths, while having at least a 1 per cent elongation in 2 inches.

While the new alloy is most useful in wrought form, such as sheets, dueto its formability charpreferable to add the calcium last and withoutthe balance being magnesium.

acteristics, it may also be suitably used in making castings, forgings,extruded forms, and the like. It is further pointed out that my newalloy is amenable to solution and precipitation heat treatments, which,accordingly, modify its properties.

The new alloy may be compounded in any of the ways known to the art,such as by adding the alloying ingredients to the molten magnesium undera suitable flux. The flux should be substantially free from magnesiumchloride if the calcium content of the alloy is to be above 0.3 percent. In those instances where an alloy is to be compounded containingless than 0.3 per cent of calcium, magnesium chloride may be present inthe fiux, but in this case it is usually too much stirring or agitationin order to prevent the loss of calcium into the flux.

I claim: 1. A magnesium base alloy containing from 0.3 to 12 per cent ofsilver, 0.05 to 1 per cent of calcium, and from 0.1 to 3 per cent ofmanganese,

2. A magnesium base alloy containing from 0.5 to 6 per cent of silver,0.2 to 0.3 per cent of calcium, and from 1 to 3 per cent of manganese,the balance being magnesium.

3. A magnesium base alloy containing from 6 to 10 per cent of silver,0.2 to 0.5 per cent of calcium, and from 1 to 3 per cent of manganese,the balance being magnesium.

4. A magnesium base alloy cinsisting of approximately 4 per cent ofsilver, 0.3 per cent of calcium, and 2 per cent of manganese, thebalance being magnesium.

JOHN C. MCDONALD.

